It is known to produce elemental chlorine by the reaction of gaseous hydrogen chloride with elemental oxygen, the so-called Deacon reaction. Moreover, such process can be combined with a process of chlorination wherein gaseous HCl and elemental oxygen are passed in vapor phase in contact with organic material to be chlorinated, under conditions such that the hydrogen chloride is oxidized with production of elemental or nascent chlorine which functions as a chlorinating agent. Such process is known as "oxyhydrochlorination," or "OHC."
The consumption of chlorine in the OHC process promotes oxidation of further quantities of the hydrogen chloride reactant. Representative of the earlier art in this area is an article in the publication, The Chemical Engineer, for July-August 1963 at pages 224-232 by J. T. Quant et al. A catalyst is used in such processes, especially copper chloride upon a carrier, usually a silicious carrier. Usually the catalyst is promoted by another metal chloride, especially alkali metal chloride, and/or rare earth metal chloride. For chlorination of alkanes and chloralkanes, the temperature range employed is broadly from 350.degree. to 550.degree. C.; and for alkenes the broad temperature range is 200.degree. to 350.degree. C. Ordinarily, the elemental oxygen is supplied as oxygen of air, although the process is operative with more concentrated forms of elemental oxygen. Pressures used are generally about atmospheric, but can be higher, e.g. up to 10 atmospheres.
In a modification of the "OHC" process just mentioned, fluorination can be effected upon a substance containing CCl groups, susceptible of fluorination by action of hydrogen fluoride and elemental oxygen. A variant is to expose a substance containing CH groups--susceptible of chlorination by elemental chlorine--to gaseous HCl and elemental oxygen under conditions suitable for producing chlorine; and to include hydrogen fluoride in the vapor phase to react with the chlorinated organic material thus formed. Such process is known as "oxyhydrochlorofluorination," or "OCF."
A representative disclosure of an OCF process is in British Pat. No. 745,818 of Mar. 7, 1956 to National Smelting Company Limited. In that patent the catalyst is aluminum fluoride impregnated with cupric chloride. Whitman U.S. Pat. No. 2,578,913 of Dec. 18, 1951 relates to oxidative fluorination of hydrocarbons by action of oxygen and hydrogen fluoride, using in most examples a catalyst of copper oxide supported on alumina; and disclosing also (column 5, lines 23-35) use of oxides or salts of metals such as copper, lead, chromium, and iron group metals supported on alumina, calcium fluoride, or copper gauze; also copper chromite.
Problems which have been encountered in employing such processes commercially arise from the fact that the copper chloride has enough vapor pressure at the required temperatures so that it migrates by sublimation, being carried downstream from its original position on the support. If in order to reduce the temperature required for reaction, the copper chloride is admixed with promoter salts such as potassium chloride, lithium chloride, rare earth metal chlorides and the like, eutectic compositions are formed which melt at the reaction temperatures generally required for these processes. To the extent that these volatilize and are redeposited downstream in solid form, they tend to block off passageways through the catalyst. Consequently the known catalysts for OHC and OCF reactions usually show markedly decreasing catalytic effectiveness with continuing use. Moreover, when the supported melt phase catalysts are used in particle form, as in fluid beds, the fusible constituents tend to cause catalyst agglomeration. Furthermore, the volatile and molten compounds, at the reaction temperatures, are highly corrosive even toward corrosion resistant construction material such as nickel-chromium alloys.
Attempts have been made to minimize these problems by obtaining more active catalysts, which would operate at lower temperatures than usually required; or by obtaining the copper catalyst in a stabilized active form, sufficiently stable at the reaction temperatures to avoid sublimation and melting during use. These prior efforts have not been sufficiently successful, at least with alkane substrates, to allow the general commercialization of such processes under existing economic conditions.